The proposed research will initiate an investigation into the origins of sex differences in behavior by observing behavioral interactions of mother rats and their male and female offspring. Specifically, the maternal behavior of mothers of all-female and all-male litters will be compared to determine whether male and female pups receive differential stimulation from such matermal behaviors as licking, handling, and body contact. Mothers of mixed-sex litters will be given choice tests to determine if one sex is preferentially retrieved; the effects of previous maternal experience on behavior in this test will also be assessed. If differences in maternal reactions to male and female offspring are found, newborn female pups will be injected with testosterone propionate and compared in their effects on maternal behavior with oil injected male and female pups. This will determine if the early androgen present in male pups provides the basis for sex differences in mother-young interactions. By comparing the behavior of anosmic mothers toward their male and female young with that of intact mothers, it will be determined if differences are due to sex differences in the olfactory stimulative properties of the young.